As far as the oil is concerned, you go by miles. It's the additives in the oil that break down from engine heat, and that takes about 3,000 miles. Those include detergents, seal conditioners, rust inhibitors, and friction modifiers.
If you drive the car very little, then time becomes more important. The additives don't wear out in the cold engine any more than they do when the oil is still in the bottle. This is where moisture condensed in the engine is an issue. That can reduce the oil's ability to lubricate, meaning isolating metal parts from each other, and that results in accelerated engine wear. The oil should be changed at least every six months to get that condensation out.
Be aware too that Ford and one other manufacturer are well-known to have two vastly different maintenance schedules for "light duty" and "severe duty". If you drive mostly at highway speeds, mostly at city speeds, mostly short-trip driving, mostly long-trip driving, or you drive on dirt roads, you fall under the "severe" schedule. No one can possibly meet all the conditions to fall under the "light duty" schedule, but that is what they go by to advertise a lower cost of maintenance than their competitors. It's a trick they use but the "light duty" maintenance schedules should be ignored.
Friday, January 17th, 2014 AT 11:36 PM